Inflammatory myopathies are conditions that are characterized by chronic muscle inflammation and muscle weakness. Muscular dystrophies are degenerative muscle diseases caused by a mutated dystrophin gene, but an underlying cause of the progressive degeneration is muscle inflammation. The inflammation associated with these diseases can damage muscle fibers, causing fatigue, pain, and progressive muscle degeneration. Regulatory T cells (Tregs) are a specialized subset of T cells. Tregs suppress activation of the immune system and thereby regulate the self-tolerance of the immune system. Subsets of Tregs expressing defined molecular markers, such as the receptor ST2, are found in inflamed tissues, such as injured skeletal muscle and inflamed lungs. Expansion and activation of ST2-expressing Tregs have been implicated in the resolution of acute muscle injury and of muscle inflammation associated with muscular dystrophy. Additionally, ST2+ Tregs are found in tissues such as visceral adipose, colon, and lung, and possess immunoregulatory and tissue repair functions in those tissues.